Production of expanded moldings of olefin polymers

ABSTRACT

A PROCESS FOR THE PRODUCTION OF MOLDINGS OF EXPANDED POLYMERS OF OLEFINS HAVING TWO OR THREE CARBON ATOMS IN WHICH THE EXPANED PARTICLES OF THE POLYMER, WHICH CONTAIN CROSSLINKED PORTIONS, ARE HEATED IN MOLDS AND FUSED TOGETHER, IF DESIRED UNDER PRESSURE.

nited States Patent Oflice 3,823,213 Patented July 9, 1974 U.S. Cl.264-51 6 Claims ABSTRACT OF THE DISCLOSURE A process for the productionof moldings of expanded polymers of olefins having two or three carbonatoms in which the expanded particles of the polymer, which containcrosslinked portions, are heated in molds and fused together, if desiredunder pressure.

This is a continuation of application Ser. No. 631,603, filed Apr. 18,1967 and now abandoned.

This invention relates to a process for the production of moldings ofexpanded olefin polymers in which expanded particles of the polymer areheated and fused together in molds.

To prepare moldings having a cellular structure, a method has been verywidely used in industry in which a styrene polymer containing anexpanding agent is first pre-expanded and the pre-expanded compositionafter a short storage period is heated inside a mold so that theparticles expand and fuse together to form a molding whose dimensionscorrespond to those of the cavity of the mold used. By this method it ispossible to prepare moldings having intricate shapes such as are usedfor example as packaging components. This method is however restrictedto styrene polymers. It has hitherto not been possible to fuse togetherother cellular polymers, for example olefin polymers, in molds withequally satisfactory results.

Expanded olefin polymers having a closed-cell structure are obtained forexample by a method in which the polymer is mixed with an expanded agentin continuous mixing equipment, for example in an extruder, and themixture is released from pressure upon leaving the extruder die. By thismethod it is possible with certain expanding agents to obtain cellularparticles or sheeting whose bulk density is from 20 to 50 grams/liter.According to another method, olefin polymers are heated in a mold underpressure with expanding agents which decompose into gaseous productswhen heated; the molding obtained is cooled, removed from the mold andthen reheated to a high temperature, thus causing it to expand.

We have now found that expanded moldings of olefin polymers can beprepared particularly advantageously by heating expanded particles ofolefin polymers which contain crosslinked portions in closed molds sothat they fuse together.

It is a special advantage that, when the expanded particles of olefinpolymers containing crosslinked portions to be used according to thisinvention are heated and fused together, moldings having a cellularstructure are obtained whose shape corresponds to that of the mold used.It is possible in this way to obtain moldings having relativelyintricate shapes and a closed-cell foam structure by a simple method.

Crystalline olefin polymers for the purposes of this invention aredefined'as polymers having crystalline regions of olefins having two orthree carbon atoms whose X-ray crystallinity at 25 C. is more than 25%.Homopolymers of ethylene or propylene or copolymers of these monomersare thus suitable for the process. Copolymers of ethylene with otherethylenically unsaturated monomers which contain at least 50% by weightof olefin units are very suitable for the process. Copolymers ofethylene with 5 to 30% by weight of esters of acrylic acid ormethacrylic acid with alcohols having two to eight, particularly two tofour, carbon atoms, or vinylcarboxylic esters of carboxylic acids havingtwo or three carbon atoms are specially suitable. Of the comonomers,esters of acrylic acid with n-butyl alcohol and with tertiarybutylalcohol, as well as vinyl acetate are of particular importance.

The expanded particles of olefin polymers for the process according tothis invention should preferably have a diameter of from 3 to 40 mm.,advantageously from 5 to 25 mm. Expanded particles are defined asparticles in which the cell membranes consist of the olefin polymer. Forthe process it is preferred to use particles having predominantlyclosed-cell structure. The expanded particles are obtained byconventional industrial methods, for example by mixing an olefin polymerwith an expanding agent in an extruder and extruding the mixture througha die, the extrudate containing expanding agent thus obtained beingcomminuted immediately after it leaves the die. It is also possiblehowever to use particles which have been obtained by heating mixtures ofolefin polymers and those expanding agents which decompose with theformation of gaseous products.

The expanded particles contain crosslinked portions, i.e. some of themolecules are present in crosslinked form so that the particles containinsoluble portions, the socalled gel content. Particles of olefinpolymers which have a gel content of 10 to 88% by weight, preferably 30to by weight, are particularly suitable for the process. Gel content isdefined as the percentage by weight of the polymer which is insoluble insolvents at temperatures above the crystallinity melting point. Solventsare used in which the polymer containing no crosslinked portions issoluble. In the case of ethylene copolymers the gel content may bedetermined for example by heating the particles in toluene to atemperature of C. and filtering off and drying the insoluble fraction.

The expanded particles containing crosslinked portions may be obtainedby various methods. Of these, a method in which the expanded closed-cellparticles are treated with high-energy rays, particularly X-rays andelectron rays, has proved to be particularly suitable. In oneparticularly suitable method of preparing the particles the particulateolefin polymer is treated with electron rays the dosage of which is from2.5 to 60, preferably 40 to 50, megarad. (1 megarad is 10 rad, 1 radbeing the absorbed energy of 100 erg per gram.)

It is also possible however to use expanded particles having crosslinkedportions which have been obtained by reaction with compounds whichdecompose into free radicals. Thus for example particles may be usedwhich have been prepared by comminuting moldings such as are obtained byexpanding mixtures of ethylene polymers and expanding agents whichdecompose with the formation of gaseous products. Sometimes it isadvantageous to add to such mixtures peroxides which cause a furthercrosslinking of the molecules. For example the comminution products ofmoldings of olefin polymers which have been obtained by expansion usingazodiisobutyronitrile are suitable.

The particles of expanded olefin polymers may contain in addition to thepolymers other components, such as flame retardants, dyes, fillers,lubricants or other polymers, for example polyisobutylene. Sometimes itis advantageous to process the expanded particles mixed withcourse-grained or fibrous filers or reinforcement materials. Examples ofthese are wood fibers, other porous materials or fibers ofthermoplastics. Coarse-meshed fabric or lattices, for example ofthermoplastics, may also be incorporated in the moldings asreinforcement materials.

Heating of the particles is carried out in closed molds. Closed moldsare defined as molds whose walls are firmly connected and which shouldbe so designed that, when the particles are heated, the gaseous orliquid substances, such as air or water, may escape from the mold butthe expanded particles cannot escape. It is advantageous to use moldswhose walls are perforated or are provided with small-bore nozzlesthrough which the heating medium may enter the mold and air may escape.The particles can be fused together in the molds Without the use ofpressure.

A molding is obtained in which the particles are fused together in aloose mass so that interstices are present between the particles. It isusually advantageous however to fuse the particles together underpressure. In a particularly advantageous embodiment of the process moldsare used at least one wall of which is movable so that the contents ofthe mold may be compressed before, during or after heating. Aparticularly advantageous procedure is first to heat the particles andthen to compress them. According to a particularly advantageousembodiment of the process the particles are compressed from two sides ofthe mold toward the center thereof. It is also possible however tocompress the particles from a number of directions, for example firstfrom two sides and then from the base or the top. In particular,moldings having relatively large dimensions may be obtained by thismethod.

Closed molds also include continuous shaping equipment such as is usedfor the continuous production of moldings of particulate expandedplastics. Such equipment may for example consist of four conveyor beltsso arranged that they form a channel. The particles are introduced atone end of this channel, then expanded and the resultant strand ofexpanded plastic is discharged at the other end of the channel. Theconveyor belts may be arranged in such a way that the particles arecompressed prior to being fused together. The conveyors may also be ofthe apron type. To prepare wide sheeting, only two parallel conveyorbelts are usually necessary, rigid or movable walls being arranged atthe sides so that a channel is formed.

The expanded particles should be heated in the mold to a temperature atwhich they fuse together. This temperature is dependent on the chemicalconstitution of the polymer, on the degree of crosslinking and on theother additives.

In order to fuse the particles together, they are advantageously heatedto temperatures at which at least 25% of the crystallite present at roomtemperature (25 C.) has melted. It is particularly advantageous to usetemperatures of from 90 to 140 C.

When copolymers of ethylene with acrylic esters or vinyl acetate areused, the processing temperature is advantageously from 90 to 135 C.

Heating of the particles in the mold may be carried out with differentheating media. Thus for example it is possible to introduce hot gases,vapors or liquids into the mold. It is particularly advantageous toplace the molds whose cavities have been filled with the expandedparticles in liquids in which the polymers are insoluble. Examples ofparticularly suitable heating liquids are Water, glycerol or aqueoussalt solutions. A simple method consists in passing hot steam into themold. The particles in the mold may also be heated by infrared radiationor by introducing 58: air. It is also possible to coat the particleswith small amounts of a substance which has a high dielectric loss, forexample water or aqueous salt solutions, and to heat them in a highfrequency field after they have been introduced into the mold.

A particularly advantageous method of heating the particles is to passthe heating medium through the mold cavity. The heating medium isadvantageously introduced at one side of the mold and allowed to leaveat the opposite side. In preparing intricate moldings, it is sometimesadvantageous to allow the heating medium to enter the mold at a numberof places and to withdraw it at one side, for example at the base of themold. According to an advantageous method which saves energy the heatingmedium is recycled through the mold. This method has proved to beparticularly suitable when carrying out the process continuously.

It is however, also possible to carry out heating by probes orperforated tubes located between the expanded particles so that heatingis effected from the interior of the mold cavity; this type of heatingmay be used additionally. Heating may thus be intensified and theworking cycle shortened, particularly in the case of large moldings. Theprobes are removed prior to compression of the particles.

The heating media may be liquid or gaseous. It is particularlyadvantageous to use water or aqueous solutions, for example of salts orhigh boiling point liquids which are miscible with water. Of the gaseousmedia, mixtures of air and steam have proved to be particularlysuitable.

According to a particularly advantageous method of carrying out theprocess the particles are compressed in the mold by 5 to 70%,advantageously by 40 to 60%, of their original bulk volume. Theparticles may be compressed before, during or particularly after theyhave been heated. Depending on the pressure used, moldings of fusedparticles are obtained between the particles of which there areinterstices or which constitute homogeneous moldings. During compressionthe particles are so deformed that they form polyhedrons which are fusedtogether at their surfaces.

After the particles have been fused together, the moldings are allowedto cool to temperatures which are below the crystalline melting point,advantageously below 40 C.

The resultant moldings may be reheated after they have been removed fromthe molds so that they further expand, thus forming a molding having alower unit weight. The moldings may also be comminuted and the particlesobtained reheated in molds under pressure.

It is possible, by using ethylene copolymers, to obtain moldings whichare flexible and whose unit weight is from 15 to 30 kg./cubic meter;this was impossible by prior art methods. The moldings have particularlygreat shock elasticity and low compression set. Expanded plasticsprepared in this way may be used with advantage in many fields. Forexample upholstery, packaging components, thermal and sound insulationin buildings, floating intermediate flooring or toys may be prepared bythe process according to the invention. The moldings may also be cut bymeans of a heated metal wire into individual sections, for example intofilms or sheeting.

The invention is illustrated by the following Examples in whichpercentages are by weight.

EXAMPLE 1 Loose spherical particles having a diameter of 20 mm. and abulk density of 16 grams/liter made of an expanded copolymer havingsubstantially closed-cell structure and derived from 83% of ethylene and17% of tertiary-butyl acrylate are exposed to radiation of 60 megarad inan electron accelerator. After this treatment, the gel content is 84%.These particles are placed in a perforated metal mold capable of beingtightly closed and having one wall which is movable, and are compressedby about 50% of their original volume. The closed mold is kept for tenminutes in water at f C. A coherent, homogeneous, very flexible, highlyelastic, extensible and tear-resistant expanded plastic having a unitweight of 32 grams/liter is together. The molding is eminently suitableas upholstery material.

When closed-cell particles consisting of a mixture of 90 parts by weightof the same copolymer and 10 parts by weight of polyisobutylene having amolecular weight of 150,000 are used instead of the said copolymerparticles, the expanded plastics obtained under the same irradiation andprocessing conditions are particularly soft and flexible.

If the particles are compressed by 70% of their original volume, aparticularly compact molding is obtained.

EXAMPLE 2 A copolymer derived from 80% of ethylene and 20% of vinylacetate is mixed in an extruder with a low boiling point hydrocarbonmixture with the application of heat and pressure. The hot mixture isextruded through a die and comminuted. The particles expand after theyhave been comminuted. They have a bulk density of 35 grams/ liter and adiameter of 10 mm. The particles thus obtained are exposed to electronradiation of 50 megarad. After being subjected to this treatment, theparticles have a gel content of 68 to 70%.

The particles are introduced into a metal mold provided withperforations which is then closed. The mold is heated for thirty minutesin a steam autoclave at a temperature of 125 C. The particles are thencompressed by 30% of their original volume and cooled in this condition.A coherent, partly air-permeable expanded plastic is obtained havingvery good mechanical and elastic properties'which is suitable forexample as shock-absorbing material in the packaging industry or forinsertion beneath [floating intermediate flooring to reduce the noise offootsteps.

if the particles are compressed by only of their original volume, amolding is obtained in which the particles are fused together at onlyrelatively small areas of their surfaces.

EXAMPLE 3 Expanded particles having substantially closed-cell structureof a copolymer derived from 75% of ethylene and 25% of n-butyl acrylatehaving a diameter of to mm. and a bulk density of 21 grams/liter areexposed to radiation with X-rays until the gel content is 75% Theparticles thus treated are placed in a metal mold having perforationsthrough which steam is introduced into the mold. Steam under a pressureof 0.5 atmosphere gauge is injected into the mold for two minutes. Theparticles are then compressed by 50% of their original volume and leftfor fifteen minutes at room temperature in this condition. A coherent,highly flexible, homogeneous expanded plastics molding is obtainedhaving a unit weight of 42 grams/liter.

Moldings can be obtained in the same way from particles having a gelcontent of 10 or 25%.

EXAMPLE 4 A mixture is prepared on rollers at 110 C. from the followingingredients:

100 parts by weight of a granular copolymer derived from 80% of ethyleneand of vinyl acetate;

10 parts by Weight of powdered azodicarboxylic amide;

1 part by weight of powdered tertiary-butyl perbenzoate;

5 parts by weight of powdered zinc oxide;

10 parts by weight of powdered calcium carbonate; and

5 parts by weight of dibutyl phthalate.

The mixture is placed in the form of rolled sheet into a metal moldwhich is gastight when closed and is kept at 170 C. under a pressure of200 atmospheres gauge for a period of fifteen minutes. The whole isallowed to cool to room temperature and an expandable molding isobtained.'This molding is kept in a heating cabinet at 170 C. fortwenty-five minutes. A finely cellular expanded plastic is formed havinga unit weight of 22 grams/liter. The expanded plastic is broken up in across beater mill into particles having a diameter of 5 to 10 mm. andthe particles are introduced into a metal mold provided withperforations which is not gastight when closed. The mold is closed,thereby compressing the particles by about 55% of their original bulkvolume. The mold is then kept for twenty minutes at 120 C. in a bath ofglycerol. A coherent molding is obtained whose dimensions correspond tothose of the cavity of the mold, which has a unit weight of 115grams/liter and which has very good mechanical and shock-absorbingproperties.

The molding is suitable for example as a sealing material and for theproduction of floats, etc.

EXAMPLE 5 A mixture is prepared at 110 C. on rollers from the followingcomponents:

parts by weight of a copolymer derived from 83% of ethylene and 17% oftertiary-butyl acrylate;

10 parts by weight of azodicarboxylic amide in powdered form;

1 part by weight of powdered tertiary-butyl perbenzoate;

5 parts by weight of powdered zinc oxide;

10 parts by weight of calcium carbonate in powdered form; and

5 parts by weight of butyl phthalate.

The mixture in the form of a rolled sheet is placed in a metal moldwhich is gastight when closed and kept for fifteen minutes at 170 C. anda pressure of 200 atmospheres gauge. The whole is allowed to cool toroom temperature and an expandable molding is obtained. This molding isbroken up mechanically into particles having a diameter of 3 to 8 mm.These particles are kept for twenty-five minutes in a water bathcontaining salt at C. The particles expand to closed-cell particles oflarger size having a bulk density of 60 grams/ liter.

The pre-expanded particles are placed in a metal mold which is notgastight when closed and are heated by injecting steam through theperforations. The particles are compressed while hot. A coherent, highlyflexible expanded plastics molding is obtained having a unit weight of120 grams/liter which is eminently suitable for the manufacture ofbuoyancy members.

EXAMPLE 6 Polyethylene having a specific gravity of 0.918 and a meltindex of 1.5 is mixed on mixing rollers at C. with an addition of 0.30%of dicumyl peroxide, 10% of azodicarboxylic amide and 5% of powderedzinc oxide to form a homogeneous composition which is removed in theform of a rolled sheet. The rolled sheet is placed in superposed layersin a gastight mold and subjected for thirty minutes in the closed moldto a temperature of 170 C.; it is then cooled. An unexpanded molding isformed. This is kept for thirty minutes in hot air at C. A finelycellular expanded plastics molding is thus formed which has a gelcontent of 75 The expanded plastics molding is broken up into particleshaving a diameter of 5 to 10 mm. The particles have a bulk density of 30grams/ liter.

The resultant expanded plastics particles containing crosslinkedportions are introduced into a cylindrical perforated metal mold havinga base diameter of 30 cm. and a height of 35 cm. and compressed to aheight of 17.5 cm. The mold is kept in this condition in a bath ofglycerol for fifteen minutes at C. The molding is then removed from themold and cooled to room temperature.

A homogeneous expanded plastics molding having a unit weight of 60grams/liter is obtained which is distinguished by good flexibility andfavorable mechanical properties. It is suitable for example asshock-absorbing material.

7 EXAMPLE 7 Expanded particles of 60% of polypropylene and 40% ofpolyisobutylene having a molecular weight of 150,000, a particle size ofto 8 mm. and a bulk density of 13.9 grams/ liter are exposed to electronradiation of 40 megarad. The gel content after this treatment is 52%.

The particles are placed in a perforated metal mold, in whichpolytetrafluoroethylene cloth has been laid, and kept for two hours inhot air at 150 C. The particles are then compressed so that their volumeis 40% of the original bulk volume. A homogeneous molding is formed bythe fusing together of the individual particles. The molding has a unitweight of 35 grams/liter, closed cells and is very suitable asinsulating material, for example for insulating liquid containers whichare exposed to temperatures of 120 C.

EXAMPLE 8 Expanded particles are prepared from the following mixture:

87% of polyethylene (apparent density 0.918; melt index 10% ofchloroparatfin;

5% of antimony trioxide; and

3% of talc.

The expanded particles have an average diameter of 8 mm. and a bulkdensity of 14 grams/liter. They are exposed to electron radiation of 5megarad. After this irradiation the gel content is 16%.

The particles are thereafter placed in a metal mold provided withperforations and having a lining of perforated sheets made frompolytetrafluoroethylene and are kept for ninety minutes at 135 C. in hotair.

The particles are then compressed to 45% of their orig inal bulk volumeand cooled for fifteen minutes at room temperature. A homogeneousmolding having a unit weight of 32 grams/ liter is removed from themold; it is soft and flexible and has very low thermal conductivity. Theexpanded plastic formed is self-extinguishing (i.e. it ceases to burnwhen removed from the igniting source).

The expanded plastics molding may be cut up into sheets of differentsizes and thicknesses with a band saw. Sheets or sections of sheets areuitable for example -as carpet underlays, for roof insulation and forjoint sealing in the building industry, as interlayers in the soil inthe construction of sportsgrounds and roads, and as structural orinsulating material in railroad cars, automobile bodies and ships.

EXAMPLE 9 Closed-cell expanded particles of polyethylene (specificgravity 0.928, melt index 0.1 to 0.3) having a particle size of 5 to 10mm., a gel content of 50% and a bulk density of 17.2 grams/liter areplaced in a metal mold synthetic materials, for insulatingmaterials,packings and the like, for example as floats, packagingcomponents, upholstery material and insulating material for cold-storageapplications and for the building industry.

EXAMPLE 10 A metal mold having six perforated surfaces and a cavitymeasuring 60 x 60 x 30 cm. is filled with expanded plastics particleshaving an average diameter of 8 to mm. and a bulk density of 17grams/liter. The particles consist of a mixture of 78% of a copolymer,which is derived from 77.2% of ethylene and 22.8% of tertiarybutylacrylate, 19% of polyisobutylene having a molecular weight of 150,000and 3% of tale. The particles contain crosslinked portions. The gelcontent is The mold is so designed that the upper and lower surfaces canbe moved toward the center of the mold. The top of the mold is attachedto a casing .through which water can be passed which then enters thecavity in the mold through the perforations in the plates.

Water at 92 C. is'introduced into the cavity of the mold through the topfor a period of five minutes. The water leaves through the sides and thebottom after it has flowed round the particles. The top and bottomarethen moved simultaneously toward the center of the cavity of the mold sothat the particles are compressed into a spacemeasuring 60 x 30 x 30 cm.The mold is opened five minutes later. A molding is obtained having aunit weight of 33 kg./cubic meter. It is cut up into sections having athickness of 3 cm. by means of a band saw. The sheets obtained have goodflexibility and high resilience. The may be used as shock-absorbingpackaging material, as insulating material or for the production oflifejackets.

EXAMPLE 11 A mold constructed as described in Example 10, and

having a cavity 50 x 50 x 25 cm. is filled with particles having a meandiameter of 5 to 15 mm. and a. bulk density of 14 grams/liter. Theexpanded plastics particles consist of a mixture of 88% of a copolymer,which is derived from 84% of ethylene and 16% of tertiary-butylacrylate, 9% of polyisobutylene having a molecular weight of 150,000 and3% of tale. The expanded plastics particles contain crosslinkedportions. The gel content is 75%. Air at 90 C. is injected through theperforated top and sides of the mold at a rate of liters per minute fora period of fifteen minutes. The air leaves the mold through the bottomafter having passed round the particles. The top and bottom are thenpressed toward the center of the mold cavity. A molding is obtainedwhich has the dimensions 50 x 25 x 25 cm. and a unit weight of 27kg. percubic meter. The molding is cut up into sheets with a band saw.

What is claimed is:

1. A process for the production of expanded moldings which comprises:heating polyethylene or a copolymer of ethylene with 5 to 30% by weightof the monomer selected from the group consisting of esters of acrylicacid with alcohols having 2 to 8 carbon atoms, esters of methacrylicacid with alcohols having 2 to 8 carbon atoms and vinylcarboxylic estersof carboxylic acids having 2 or 3 carbon atoms, said polymer orcopolymer having an X-ray crystallinity at 25 C. which is more than 25%and containing an expanding agent to a point sufficiently high to expandsaid olefin polymer; subjecting particles of the expanded polymer tohigh energy radiation to produce expanded particles having a gel contentof from 10 to 88% by weight; placing said particles in a closed moldfrom which gaseous and liquid substances can escape but from which theparticles cannotescape; heating said particles in said mold to atemperature at which they fuse together; and compressing said particleswithin said mold by from 5 to 70% of their original bulk volume.

2. A process for the production of expanded moldings wherein expandedparticles of polyethylene or polypropylene or a copolymer'of ethylenewith 5 to 30% by weightof' a' monomer selected from the group consistingof esters of acrylic acid with alcohols having 2 to 8 carbon atoms,esters of methacrylic acid with alcohols having 2 to 8 carbon atoms andvinylcarboxylic esters of carboxylic acids having 2 or 3 carbon'atomswhose X-ray crystallinity at 25 C. is more than 25% and containingcrosslinked portions in such an amount that from 10 to 88% by weight ofthe homopolymer or copolymer is insoluble in solvents at temperaturesabove the crystallinity melting point using solvents in which thenon-crosslinked polymer is soluble (a) are placed in a closed mold fromwhich gaseous and liquid substances can escape but from which theparticles cannot escape,

(b) are heated to a temperature at which they fuse together, and

(c) are compressed by about to 70% of their original bulk volume.

3. A process according to Claim 2 wherein the insoluble portion of saidhomopolymer or copolymer is of from 30 to 80% by weight.

4. A process according to Claim 2 wherein the said particles arecompressed from two sides toward the middle of a mold.

5. A process according to Claim 2 wherein the said particles are heatedin a mold by passing a heating medium through the mold cavity.

6. A process according to Claim 2 wherein the said particles are heatedin a mold by passing a heating medium through the mold cavity containingthe particles to a temperature at which at least of the crystallinefraction is fused and the particles are compressed by 5 to of theoriginal bulk volume of the particles.

References Cited UNITED STATES PATENTS 3,010,157 11/1961 Cizek 260-2.5 B3,250,730 5/1966 Palmer 2602.5 E 3,255,286 6/ 1966 Luc-Belmont 26451 UX3,359,353 12/1967 Oddi 264-321 X 3,379,802 4/1968 Raley 2'602.5 BX3,452,390 7/1969 Borcovec 2-64-321 X 3,098,832 7/1963 Pooley et al264--Dig. 18 3,368,009 2/ 1968 Oddi 264-53 3,504,068 3/1970 Zizlspergeret al. 26453 X OTHER REFERENCES Billmeyer, Fred W.: Textbook of PolymerScience, New York, Interscience, 1962, pp. 363-376.

Frank, H. P.: Po1ypropylene," New York, Gordon and Breach SciencePublishers, 1968, pp. 1-9.

PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

2602.5 B; 26454, 126, 321, Dig. 5, Dig. 17, Dig. 18

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3, 823,213

DATED July 9, 1974 E T0 (5) Fritz Stastny, Rudolf Gaeth & Hans-GeorgTrieschmann It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, in the heading, insert-C1aims Priority,

Applications German, April 28, 1966, P 16 29 281.2, and

August 23, 1966, P 16 29 295.8-;

Column 7, line 45, delete "uitable" and substitute suitable- Signed andScaled this sixth D y of January 1976 [SEAL] Attesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Parenrsand Trademarks

